Download Genetics - Louisiana Association of FFA







Mating animals to produce certain
characteristics
Low Birthweight
Heavier Weaning Weight
Color
Horned or Polled
Temperment



Animals are the result of Feed, Health, and
Inheritance (genetic material)
Feed is fastest to correct
Genetics last longest




All body cells contain “Blueprints” with
instructions as to how an animal will look or
act etc.
One Gene comes from each parent (pairs)
Genes are divided into sections
(Chromosomes) that carry genes
Sex chromosomes: male = XY, female = XX





Dominant Genes = one gene overshadows
the other
Angus Cattle: black is dominant, red is not
(Bb)
Hereford: white face is dominant (Ww)
Hampshire Hog: white belt is dominant
Horns are dominant (Pp)






The gene that is overshadowed by a
dominant gene
Recessive genes can only express
themselves if both genes are recessive
Polled vs Horned (Pp) (pp)
Black wool vs white (Ww) (ww)
Dwarfism vs normal size (dd)
Albino



P = horned
p = polled
If a homozygous horned cow (PP) is mated to
a homozygous polled bull (pp), what percent
of the calves will be horned, polled?
P
p
P p
p
P p
P
P p
P p

If a homozygous horned cow (PP) is mated to
a heterozygous horned bull (Pp), what
percent of the calves will be polled?
P
p
P p
p
P p
P
P p
P p





Some recessive genes are attached to the
X and Y chromosomes
Humans: Colorblindness and Baldness are
on the X chromosomes
In Men, traits expressed anytime present
In Women, must have two recessives to
show trait
Children get baldness from mothers
X
X
XX
X
XX
Y
XY
XY
Y
X B
X
X
XX
B
XX
B
X Y
XY
X
X B
X
XX B
XX
Y
X BY
XY
X
X B
X B
X X B
X X B
Y
X BY
XB
Y



If both genes express themselves
Shorthorn Cattle: Red male mated to a White
female = Roan calf
RR + WW = RW





Shorthorn Cattle
R = Red
W = white
RW = roan
If a red bull (RR) is mated to a white cow
(WW), what color will the calves be?
R
R
W
R
W
R
W
W
R
W
R
W

If a red bull (RR) is mated to a roan (RW)
cow, what color will the calves be?
R
R
R
R
R
R
R
W
R
W
R
W
R
W
R
R
R
R
W
R
W
W
W
W




Dwarfism
Monorchid = only one testicle descends
Cryptorchid = no testicles descend
Short ears & tails






Dramatically different from what is
expected genetically
Horned calf from polled parents
Loss of some or extra body parts
Lethal Mutation: causes death at birth
Sublethal Mutation: limits animals ability to
grow to maturity
Beneficial Mutation: loss of tail in lambs


Similar to a Mutation, only it is caused by
something in the environment
Siamese twins




Chance that traits will be inherited
Low: multiple births, fat covering
Medium: birth wt, wean wt, milk, wool grade,
carcass wt, rate of gain
High: Loin eye area, fleece length & quality





Currently have ewes that wean 70 lb lambs
Want to raise weaning wt to 110 lbs
Select a ram with a wean wt of 110 lbs
Heritability of weaning wt is 30%
What can you expect new lamb crop to weigh
at weaning?

What is the difference in current weaning wt
and that of the new ram?
110 - 70 = 40 lbs

Heritability % x difference
30% x 40 = 12 lbs


Can expect a gain in weaning wt of 12 lbs
70 lbs + 12 lbs = 82 lbs



Random Mating: all males have an equal
opportunity to mate with all females
Outcrossing: mating purebreds with unrelated
purebreds
Inbreeding: mating related animals
 Linebreeding: parents mated to offspring

Crossbreeding: mating animals of same
species but different breeds






Offspring will outperform either of the
parents
Corn Breed A yields 100 bu/acre
Corn Breed B yields 100 bu/acre
Crossbreed A & B yields corn that yields 200
bu/acre
Vigor only expressed in crossbreeding
Donkey mated to a horse = Mule
 mule is sterile



Animals not common to United States
Difficult to define today
New breeds are exotics




Genotype: genetic makeup (Bb)
Phenotype: physical appearance (Black)
Heterosis: Genes are different, Dominant &
Recessive (Bb)
Homozygous: both genes are the same (BB
or bb)